03-Functions-and-Strict-Mode

Day 18 – Shell Scripting: Functions & Slightly Advanced Concepts

Task 1: Basic Functions

1. Create functions.sh with:

   • A function greet that takes a name as argument and prints Hello, <name>!
   • A function add that takes two numbers and prints their sum
   • Call both functions from the script

   Script

   

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Task 2: Functions with Return Values

1. Create disk_check.sh with:

   • A function check_disk that checks disk usage of / using df -h
   • A function check_memory that checks free memory using free -h
   • A main section that calls both and prints the results

   Script

   

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Task 3: Strict Mode — set -euo pipefail

1. Create strict_demo.sh with set -euo pipefail at the top
2. Try using an undefined variable — what happens with set -u?
3. Try a command that fails — what happens with set -e?
4. Try a piped command where one part fails — what happens with set -o pipefail?

Document: What does each flag do?

• set -e → Exit the script immediately if any command fails.

• set -u → Exit the script if an undefined (unset) variable is used.

• set -o pipefail → Pipeline fails if any command fails.

  Script

  

  

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Task 4: Local Variables

1. Create local_demo.sh with:

   • A function that uses local keyword for variables
   • Show that local variables don't leak outside the function
   • Compare with a function that uses regular variables

   Script

   

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Task 5: Build a Script — System Info Reporter

Create system_info.sh that uses functions for everything:

1. A function to print hostname and OS info

2. A function to print uptime

3. A function to print disk usage (top 5 by size)

4. A function to print memory usage

5. A function to print top 5 CPU-consuming processes

6. A main function that calls all of the above with section headers

7. Use set -euo pipefail at the top

   Script

   

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What I Learned

Functions & Modularity – Learned to create reusable, organized code blocks.This makes scripts cleaner, easier to read, and simpler to maintain.

System Monitoring Scripts – Explored fetching system info like memory,disk usage,and CPU processes.Useful for building quick automation for system health checks.

Error Handling & Safety – Using set -euo pipefail to catch undefined variables,failing commands,and pipeline errors early,making scripts more reliable.

Variable Scope – Understood the difference between local and global variables. Local variables stay inside functions, while global variables affect the wider script.

Practical Automation – Using a main function to orchestrate tasks helps make scripts modular,maintainable,and automation-friendly.

Function Naming Pitfall – Faced an issue where naming a function the same as a system command (uptime) caused an infinite loop. Learned to avoid using system command names for functions.